This study investigated the effectiveness of Ai Chi compared to conventional water-based exercise on balance performance in individuals with chronic stroke. A total of 20 individuals with chronic stroke were randomly allocated to receive either Ai Chi or conventional water-based exercise for 60 min/time, 3 times/week, and a total of 6 weeks. Balance performance assessed by limit of stability (LOS) test and Berg balance scale (BBS). Fugl-Meyer assessment (FMA) and gait performance were documented for lower extremity movement control and walking ability, respectively. Excursion and movement velocity in LOS test was significantly increased in anteroposterior axis after receiving Ai Chi (p = 0.005 for excursion, p = 0.013 for velocity) but not conventional water-based exercise. In particular, the improvement of endpoint excursion in the Ai Chi group has significant inter-group difference (p = 0.001). Both groups showed significant improvement in BBS and FMA yet the Ai Chi group demonstrated significantly better results than control group (p = 0.025). Ai Chi is feasible for balance training in stroke, and is able to improve weight shifting in anteroposterior axis, functional balance, and lower extremity control as compared to conventional water-based exercise.Stroke is a cerebral vascular disease caused by the interruption of the blood supply to the brain, cutting off the supply of oxygen and nutrients 1 . Damage to the brain tissue leads to sensory, motor, cognitive, and emotional deficits. With impaired motor and sensory functions, stroke patients suffer from deficits in balance control which plays crucial role in ambulatory function and thus as an important clinical indicator 2-5 . Balance is defined as the ability to maintain center of mass (COM) within the stability limits, the boundaries of the base of support (BOS) 6 . Balance control can be quantified by limit of stability (LOS) test, expressed by movement velocity, displacement excursion, and directional control 7,8 . Individuals with stroke usually show decline in the abovementioned balance performance 9-12 . Bohannon 13 noted the correlation between static standing ability and independent mobility in stroke patients (r = 0.62). Lee et al. 14 found that walking velocity is associated with maximal displacement excursion in LOS test (r = 0.68, p < 0.01) and Berg balance scale (r = 0.66, p < 0.01) in patients with stroke. In addition, the balance-related fall risks should also be addressed in people with chronic stroke 15,16 . Therefore, it is crucial to improve balance control in order to improve the balance-related activities for individuals with stroke.Several elements, such as strengthening, postural control, weight shifting, and agility exercise, are necessary to be incorporated during balance training 17 . It has also been noted that increased somatosensory inputs and visual deprivation might exert positive effects on top of balance training, as well as enriched environment 4,5,18,19 . Water-based exercise, by utilizing the properties of water, including ...